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16 December 2011, Volume 31 Issue 5
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. 2011, 31(5): 1-4.Yushu Ms7.1 earthquake occurred in the Bayan Har block, exactly the GanziYushu fault zone. We set up a relative gravity survey lines cross the fault zone and conducted the gravity survey. We processed the raw data, such as atmospheric correction, polar motion correction, drift correction, adjustment calculation, and then obtained the free air anomaly of the profile. After the curvature correction, flatpanel and highprecision terrain correction by using the ASTER GDEM (2009) Digital terrain model (1 ″× 1″), we obtained a complete profile of the probe Bouguer gravity anomaly. The results show that the location of faults which consistents with the geological results as their is a
sudden change zone in the Bouguer anomaly curve; the basement begins to uplift from the place near Yushu to its northeast along the profile, and the maximum rate is at Qingshuihe town. We have concluded that it is resulted from the Indian crust subducting and inserting, making the eastern edge of QinghaiTibet Plateau uplifting. -
. 2011, 31(5): 5-8.On the basis of the Total Electron Content (TEC) obtained from International GNSS Service (IGS) and the VTEC derived from the GPS observation data from the reference stations of Crustal Movement Observational Network of China and using the method of moving average,we have processed and analyzed the ionospheric TEC prior to the Myanmar Ms7.2 earthquake.
The results show that the anomalous reduction of TEC occurred on 6-8 day prior to the earthquake and the anomalous increase of TEC occurred on the 3rd day prior to the earthquake may be related to the geomanetic disturbance on Mar. 21. Due to the time is close to the occuring moment of the event, it can be concluded that the observed anomalous reduction of ionospheric TEC on Mar. 16, 17 and 18 and the conjugated structure of the anomalous reduction on Mar. 18 is possibly related to the earthquake excluding the effect of solar activity and geomagnetic disturbance. -
. 2011, 31(5): 9-13.Using horizontal velocity data observed by GPS in 2009-2010 in Sichuan and its nearby areas, referring to relevant results in 2004-2007 and 2007-2008, with the aid of analysis of deformation-stain field and inversion of negative dislocation, the features of recent strain accumulation of active faults and their difference between different regions and different segments and together with the evolution of influence from the Wenchuan and Yushu earthquakes are researched.The results are as follows.1)Influence from the Wechuan earthquake decreased obviously but had not ended, at the Longmenshan fault and its two ends especially. 2)Weaker influence from the Yushu earthquake was observed. 3)At present,these regions had background of strong earthquakes, i.s., the southwestern margin of Ordos, boundary of GansuQinghaiSichuan and GansuSichuan and GansuSichuanShannxi, eastern boundary between Sichuan and Yunnan, from the northwestsen Yunnan to the boundary between Sichuan and Yunnan.
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. 2011, 31(5): 14-19.We used Wuhan, one of IGS stations, as a reference to form ultra long baseline and solve instantaneous 1HzGPS positions and measure the coseismic kinematic deformations caused by Wenchuan earthquake. Compared with the results from using Yaan as the reference which is nearby 1HzGPS stations, the deformation solutions show good consistence with different reference stations. The maximum deformation amplitude is found for station Pixian, which had the largest deformation about 1.034 meter. The deformations of stations,such as Pixian, Chengdu, Mianyang, Zhongjiang are relatively larger and also show the propagation direction of seismic waves. The smaller deformations occurred in Qionglai, Yaan, in the south of the epicenter, which indicate that the fault ruptured from the epicenter to the northeast. On the basis of the arrival time of seismic wave recorded in kinematic time series and the distance between 1HzGPS stations and the epicenter, the estimated average velocity of seismic wave in the crust is 3.1 km/s.
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. 2011, 31(5): 20-25.On the analysis of deformation information reflected by GPS velocity data in different reference, the difference between movement and deformation is discussed and we emphasize the deformation is independent from reference basis. On the basis of reliability analysis of GPS strain rate calculation results with least square collocation method, the evolution characteristics of GPS strain rate fields are discussed in different spatial scale. The eastwest strain rate fields shows that the area in west to 92°E has a EW stretch and the area in the east to 92°E has an EW compression in QinghaiTibet block. This character reflects the eastward flow of the material of QinghiaTibet plateau is barred by NorthChina and SouthChina Blocks and forms a spatial span of 900km compression zone, that the strain rate results of 3 sections shows the high compression zone locating at the middle area of SouthNorth seismic zone. The strain rate result in SichuanYunnan illustrates that the eastward movement of Bayankala block lead to the surface strain concentrating in the source of Wenchuan eartqhake, and the eastwest compression deformation becomes more intensive in Longmenshan faults while the high area of eastwest compression transferring to east. The evolution result of rotation rate fields shows that the anticlockwise deformation is weaken in the south of Longmenshan fault and the clockwise deformation has been strengthened in the north of Longmenshan fault from 2004 to 2007. The distribution of principal strain rate changing from disheveled to consistent reveals that the locking status of Longmenshan fault has reached highpoint with the compression and dextrorotation deformation strengthening.
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. 2011, 31(5): 26-29.The mechanism of the vertical uplift of crust in the west of Longmenshan before Wenchuan Ms8.0 earthquake has been debated through constructing the 2D FEM model for the profile across Longmenshan fault, which is based on the velocity field that had calculated from the GPS observations and the result of seismic tomography obtained by Wu Jiangping et al. In addition,the effect of crustal inhomogeneity on the vertical uplift has been discussed as well. We concluded that the existence of the low velocity anomaly in the low cust below the front of Longmenshan fault play a key role, and vertical uplift is likely caused by both the curst shorten of the westen Longmenshan and the differential uplift between Chuanxi pletau and Sichuan basin.
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. 2011, 31(5): 30-34.Using the GPS velocity field data during the periods of 1999—2007 and 2007—2009, we analyzed the deformation characteristics of the SichuanYunnan region during the two periods with block deformation model and by analyzing the GPS velocity profiles. The results show that the direction of the principal compressive strain rate of the westnorthern segment of Sichuan blockthe middle segment of Yunnan blockthe westsouthern segment of Yunnan block is characterized by clockwise rotation from north to south. The Anninghe fault and the Zemuhe fault have some shear strain accumulation, and the southern segment of Xiaojiang fault is mainly strikeslip, but its northern segment is mainly accumulating strain. The earthquake had relatively obvious influence on the mediumsouthern segment of LijiangXiaojinhe fault, the Anninghe fault and the Jinshajiang fault,meanwhile it affected the Zemuhe fault, the Xiaojiang fault and the Honghe fault less.
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. 2011, 31(5): 35-38.Although North China belongs to Craton type in geology, there exist quite a lot of low velocity layers (LVL) in its crust, especially in its eastern region. Most of these LVLs locate at the bottom of the upper crust with depth of 15-25 km. Compared with LVLs in active orogens, the LVLs in North China possess greatly different characteristics. Usually, these LVLs are not large in horizontal scale and are not connected each other. In the same time, the velocity drops are small, usually less than 5%. Considering the thermal erosion action at the bottom of the lithosphere and the geothermal state, it is deduced that partial melt may be one important factor to generate LVLs in the crust.
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. 2011, 31(5): 39-43.With 848 Ml≥2.0 focal mechanisms which occurred during in January,2002 to June 2010 in northern part of North China,and according to regional tectonic feature, the area is divided into four studied regions to analyze the focal mechanism features of each partitions and to research stress field feature parted by 1°×1°and with 0.5°slip trapeze zone. The results show that the maximum principle stress orientation of various studied partitions all is NEE, the minimum principle stress orientation is NNW, they are basically consistent with the direction of tectonic stress field in North China. The stress structures of various partitions all are of strikeslip type, the principle feature of tectonic stress field in northern part of North China is horizontal stress action, the way of focal strainslip way is strikeslip mainly.
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. 2011, 31(5): 44-46.By using the elevation data and Airy model, the Moho depth can be calculated. Through applying Parker’s formula, the isostasy gravity correction of the crustal deformation can be obtained as well. Therefore, the isostasy gravity anomalies gained by subtracting the corrections from observed Bouguer anomalies approximately represent the isostatic features of Chinese capital area, which plays an important role for investgating the deep structure and earthquake prediction in the future. The results show that the isostatic value which is of around ±20×10 -5 ms -2 in eastern part of capital and its adjacent areas, indicates that basically isostatic has been reached, while some places in west and north of capital area are still in unisostitc status.
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. 2011, 31(5): 47-51.
The Taiyuan basin is divided into four sections: the TaiyuanWenshui area and the Fenyang area, the Taigu area and the JiexiuPingyao area. The paleoearthquake data obtained in recent years in Taiyuan basin is analysed, with realtime probability model, the quantitative assessment of earthquake potential is carried out for above each section. The probability of earthquake occurrence in the TaiyuanWenshui area, the Taigu area in the next 50 years are 7.1%，15%，in the next 100 years are 13.9%，27.8%, while the Fenyang and the Taigu areas have very low possibility of earthquake larger than magnitude 7.
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. 2011, 31(5): 52-60.In order to quantify the effect of medium heterogeneities and the dip of the fault on the coseismic displacement, threedimensional finite element numerical method was applied. The selected slip distribution models including finite rectangular strike, normal and reverse fault.The numerical simulation has given following results.1) For the vertical strike earthquake in the homogeneous and vertically layed
mediums, the coseismic displacement slightly depends on the Poisson’s ratio, the relation between horizontally displacements and Poisson’s ratio is negative, and it is positive for the vertical displacements. The relation between horizontally displacements and shear modulus is positive, and it is negtive for the vertical displacements; 2) In horizontally heterogeneous medium, the shear modulus plays a significant role on the surface displacements, the relation between shear modulus and displacement field is negative, in the case of the medium parameters on the right block of fault remain unchanged, the increase extent of maximum vertical displacements on the left block of fault reaches 55.6%
and the shear modulus of the left block of fault halved.3)In the neighborhood of fault,the dip angle of fault dominate the coseismic displacements, as for the reverse fault earthquake with high dip (60°-90°), opposite direction region appears in the horizontal displacements on the hanging wall, the range of opposite direction region increase with dip-angle;and the increase extent of coseismic displacements on the foot wall is obvious. -
. 2011, 31(5): 61-64.We regard gravity time sequence system as slow timevarying system and use difference equations for describing its equivalent parameter model based on the theory of linear systems analysis.
By judging the stability of parametric sequence,we are going to explore the precursors.
On the basis of gravity timevarying series from 1994 to 2009 of three observation points in Hexi gravity survey network, we prove that this method is effective, but more research are required to confirm the relations between unstability and seismic precursor anomalies. -
. 2011, 31(5): 65-70.Aiming at the uncertainty of earthquake discrimination by using anomaly of fault deformation, 3 strong earthquakes in the northeast margin of QinghaiTibet block as typical examples were analyzed. In addition, the abnormal characteristics (modality、time series、spatial distributing) of fault deformation before the earthquake, the seismic activity of correlative outer tectonic region were analyzed.From these analyses the following conclusions are drawn. If the anomaly of fault deformation satisfies the criterion of abnormal characteristics before earthquake and the seismic activity of correlative outer tectonic region is strong, the possibility of an earthquake is big; otherwise little possibility of an earthquake.
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. 2011, 31(5): 71-74.After Wenchuan earthquake,Niumiangou valley becomes an area with dense and frequent debris flow disasters; so far, seven largescale debris flows occurred. In this valley there are three basic conditions making debris flow well develop,
and so it is in a developing stage now.Thus the largescale rainfall induced debris flow disasters, with large damage and stronger wallop, will easily occur in the 5-10 year after earthquake. If considering to use directly the debris flow deposit in the main gully of Niumiangou valley, to construct civil control engineering such as alternate landslide dams from earth and rock with about half of main gully width in the left and right sides of upper and middle of the accumulation area, landslide dams from earth and rock with approximately equal to main gully width in middle and lower of the accumulation area and slope with certain gradient and relative to gully orientation between two adjacent dam, then the dualpurpose of energy dissipation and consumption can be achieved. -
. 2011, 31(5): 75-79.From the analysis of colleted data of NGA’s regional geological survey on editing time, the record content in the geological data, the survey organization, purpose, means, methods etc. of the survey,it can be seen that there are some differences and these differences can be divided according to: the bud stage; initial stage; great period of development, and digital mapping period.
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. 2011, 31(5): 80-83.]In traditional plane fitting methods for point clouds, people don’t consider errors in data and in coefficients matrix simultaneously, which will result in incorrectness of plane parameters. In order to overcome this shortcoming, a new method for fitting local plane to point clouds was proposed. The method is based on total least squares. In consideration of the errors in all observation data, we tried to delete outliers from point clouds, and thus obtained a robust solution to plane fitting parameter. Analytical experiments based on simulated data and real data were conducted, and comparisons between the method and traditional methods such as least square method and eigenvalue method were also implemented. The results show that the method has the capability to overcome bad influence from outliers, and to increase the reliability of parameters estimation.
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. 2011, 31(5): 84-87.The accuracy of horizontal velocity measured by GNSS mobile observation was evaluated by continuous observation, and the effects of difference of observation time period between two adjacent observations, observation time and observation cycle on the accuracy were also analyzed. The results show that, according to the current observation style, the absolute value of difference of horizontal velocity between mobile and continuous observation is less than 3mm/a. The difference of observation time period between two adjacent observations can affect the accuracy of horizontal velocity. If the difference which is less than 3 mm/a can be accepted, it is suggested that the difference of observation time period in the two years should be less than 25 days. The accuracy can be improved by prolonging observation period and shortening observation cycle.
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. 2011, 31(5): 88-90.]In GPS height fitting, a new method of Weighted Total LeastSquares adjustment (WTLS) is presented for solving the error of coefficient matrix. A more reasonable fitting model of plane and quadric polynomial is established, and the corresponding iterative algorithm is given. The examples of calculations show that the polynomial parameter is more reasonable and the solved height anomaly is more accurate.
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. 2011, 31(5): 91-96.After summarizing the classification methods of polynomial model, the linear transformation from a unit circle to any ellipse or circle is studied, thus the polynomial model based on linear transformation is derived. By comparing the polynomial model based on linear transformation with the traditional scalar polynomial model on the number of items, the model parameters, calculation properties and the collection of objects that can be represented by model, as well as giving an analytical example about the plane circle fitting,it is found that the new model has a more compact form, its parameters have perceptual geometric meaning and good operational properties, it is more suitable for the expression of the higher-dimensional and higher-degree polynomial object. Particularly it is more convenient to obtain the necessary parameters in industrial surveying field. On the whole, the polynomial model based on linear transformation has more advantages.
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. 2011, 31(5): 97-100.
n order to satisfy the accuracy requirements of the earth dynamical form factor (J2) needed in satellite orbit determination, weapon launch and the calculation of astronomic constants, the value of
J2 was estimated from the secular trends of the orbits series of three gravity satellites. The factors such as orbit height, sampling interval and the disturbing forces were studied. The results show that the higher orbit produces the better calculation accuracy. Besides, that all disturbing forces on GOCE orbit considered reduces the calculation accuracy.
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. 2011, 31(5): 101-105.According to the characteristics of satellite altimeter waveforms, a new classification of radar altimeter waveforms, called minimum distance, is presented. The method based on the principle of dynamic cluster analysis can efficiently classify the radar waveforms by using moving minimum Euclidean for similarity index. Topex/Poseidon coastal waveforms across Taiwan strait are applied to comparatively analyze the classification results of pulse peakiness and Beta5, and the feasibility of the classification is verified, and K value of reasonable coastal altimeter waveforms classification is determined.
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. 2011, 31(5): 106-110.In the autonomous orbit determination, we need EOP uploaded by ground station to achieve translation of Conventional Terrestrial System and Geocentric Celestial Reference System. However, when the satellite navigation system gets into autonomous navigation mode, the ground station can not upload the latest EOP, the system can only use longterm prediction of EOP. EOP prediction error will affect the ephemeris offered by the autonomous navigation system, and ultimately affect positioning accuracy of users. EOP prediction errors, the influence of EOP prediction errors to autonomous navigation system orbit ephemeris and positioning accuracy of users are discussed and analyzed. The results show that the prediction error of EOP almost has no influence on the radial error of satellite orbit and satellite clock error in long-term (110 days) autonomous orbit determination. It mainly influences the Plane Error (Along Error and Cross Error) and URE (User Range Error) and these errors show a certain periodicity. Moreover, these errors mainly influences NorthSouth direction error and EastWest direction error in pseudorange positioning.
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. 2011, 31(5): 111-113.By using the data of CMONOC and fitting the ionosphere VTEC model， a method of predicting ionosphere TEC with discrete Kalman filtering is provided.In the case of prediction and analysis of the particular time in September 10,2002 and September 14,2002，the accuracy of prediction is 2.5TECU around，so we can offedively predict some ionosphere activities with the method.
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. 2011, 31(5): 114-118.The longterm variations of a variety of GPS receivers’ DCB were analyzed based on the DCB published by the Center for Orbit Determination in Europe during 2001—2009. The results show that there are periodic behaviors in the timeseries of the change receivers’ DCB, among then the monthly and yearly periods are the most predominant. In addition, certain fluctuations underlying the longterm behaviors in GPS receivers’ DCB can also be found, and some of the GPS receivers may suffer the deterioration of DCB stability, or even somewhat deviation.
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. 2011, 31(5): 119-122.The implement of a basic SAR (Synthetic Aperture Radar) data processing platform is extremely important for coherence analysis by using SAR image in the earthquake disaster area. After demanding analysis, methods research and workflow design,
a kind of user interaction platform based on Windows and VC ++6.0 is introduced. The functions of this platform mainly contains data inputting, image registration, coherence analyzing and estimating，and so on . The results show high reliability and high efficiency of the platform for processing ERS (European Remote Sensing Satellite) data. -
. 2011, 31(5): 123-127.The massive satellite data presents a significant computational challenge to estimate the gravity field. Analyzing the computingintensive tasks in recovering the earth gravity field model based on the direct least-squares algorithms, on applying parallel computing techniques capable of rigorously inverting geopotential coefficients using direct method on the basis of OpenMP is focused. Eventually, the earth’s gravity fields complete to degree and order 60 are recovered respectively on the basis of monthly along track disturbing
potential observations and gravity gradient observations (with 5 s sampling interval). The simulation shows that introducing the parallel algorithms based on OpenMP into determination of the earth’s gravity field model can be more effective, and is of great reliability. -
. 2011, 31(5): 128-131.On the basis of the analysis of impect factors of surveying accuracy of RTK, focusing on analyzing measurement error caused by human factor i.e. centering rod tilt, a new method which is by surveying spherical coordinates and fitting sphere centre coordinates to calculate measured point coordinates is put forward.Through examples, compared with GPS static observation, the error of RTK method is of less than cm level. This not only proves that RTK fitting sphere centre can avoid the error caused by centering rod tilt, but also improves RTK plane accuracy to a certain extent.
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. 2011, 31(5): 132-135.The recursive least squares algorithm for dynamic regression model, which can be used in the online regression modeling for dynamic data sets, is deduced. When the new observations updating, the dynamic regression algorithm, by avoiding the increment of matrix size, and avoiding the computation of the inverter matrix, can decrease the computation time of solving model parameters. The algorithm is easy to be programmed and no iterative computation is needed. The simplicity and practicality have been verified by using the dynamic regression approach in Zhexi and Dongjiang Dam deformation prediction samples. By compared with other algorithms, the method can reduce computation time and improve prediction precision.
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. 2011, 31(5): 136-140.By combining wavelet transform with STFT,finely decomposing the part of signal of high frequency from the part of low frequency has been realized and the timefrequency spectrum of the high frequency of the signal is given in the same time.Its results are direct and clear and the computational course is simple.
This method can be used not only for analyzing continuous deformation observation data as a conventional method, but also can be used
for other continuous observations. -
. 2011, 31(5): 141-145.On the basis of the study of crossfault mobile deformation monitoring environment in the Capital Region of China,
it is found that there are a few sites(near 20%) impacted by the nonseismic factors.
So we suggest that the crustal deformation monitoring techniques(instruments) and the crossfault deformation surveying line layout
should be improved and the crossfault flow deformation level ling survey and baseline level of observation should be at the same pile. The baseline survey pile of existing level and baseline measurements should be technologically transformed at the appropriate time,in the measurement instrumentation: DiNi electronic level should be used instead of Ni002 Optical Level, Di2002 even TC2003 and TCA series of instruments should be used instead of the 24m traditional foot baseline deformation monitoring. -
. 2011, 31(5): 146-150.The newest generation of gPhone spring gravimeter of Microg LaCoste Inc. is the major observation instrument of China earthquake monitoring network.
In this paper, We use M2 tidal wave amplitude factor from the tidal analysis from long period observation data of SGC053 superconducting gravimeter to determinate the calibration factor of 28 colocated gPhone spring gravimeters which passed the test at the some place. The results show that the calibration factor of these instruments are between 0.999 9 and 1.019 6, and that the calibration factor of instrument had been determined before they leave the factory but now is subtlely changing because of new observation location. We analyzed and processed the observation data after correction again. The precision of M2 tidal wave factors are better than 0.8‰, the non tidal gravity change in time series of residual with drift correction is (4-10)×10 -8 ms -2, amplitude of diurnal wave is less than 0.1×10 -8 ms -2, and amplitude of semidiurnal wave is less than 0.3×10 -8 ms -2, so it is proved that the results are well improved after determination. It is indicated that gPhone spring gravimeters can be used for the observation under a unified tidal datum by using precise M2 tidal wave factor to determinate the calibration factor of instrument, further it can provide accurate observation data of gravity change for earthquake monitoring by gravity and scientific research. -
. 2011, 31(5): 151-155.Using samesite observations obtained with the SGC053 superconducting gravimeter and the gPh058 gravimeter in Gravitation and Earth Tide Observatory of China (GETOC), the scale value (alias calibration factor) of the gPh058 gravimeter is accurately determined with the Chebyshev polynomial model. Through the analysis of regression order, sampling number, sampling time, the most obvious affect factor is the sampling time. The weighted average scale factor of different sampling times is 1.008 4±0.00 09×10 -8 ms -2/mV. Compared with the harmonic analysis before determination, the numerical results show that tidal parameters of comparatively high accuracy can be achieved with the gPh058 gravimeter. After determination, the amplitude of the residual with synthetic tide and drift correction is only 1/4 of that as before. Although gPh058 gravimeter had been calibrated in factory, the samesite determination should be more reliable.
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. 2011, 31(5): 156-159.The advantages of infrared sensing technology in measuring gas from fault zones, the structure of the instrument, the technical performance, and the ways for overcoming its disadvantages are discussed. Through analyzing the observations with infrared gas instrument at experiment station, a new infrared instrument for measuring gas from fault zones is explored.
